Payment-processing service Square said Monday that it debuted Square Appointments to its register service. Square Appointments allows merchants' customers to make and book appointments online, saving staff time.

Such online scheduling services from rivals have been popular with hair salons, tutoring services and others. San Francisco-based Square has an advantage over those rivals in that Square Register now includes that ability as part of its growing list of services for merchants.

That's a significant advantage for the company, which is seeking to justify its $5 billion valuation garnered in its last round of financing. Square is among several startups competing with tech and finance giants for a piece of the payments business.

Square Appointments, like Square Feedback, comes with an additional monthly charge for merchants. It costs $30 a month for individual sellers, $50 for businesses with two to five employees and $90 for unlimited staff. The appointments feature is also available to businesses of all sizes, even those not using Square Register.

Square's initial test of Square Appointments confirmed what anyone who has ever booked or changed their own appointment online already knows: it's popular.

A survey of 200 businesses that participated in Square Appointments' pilot found that 72 percent of sellers said the system helped generate additional revenue, 62 percent saved a half hour each day, and 54 percent said the number of appointments per week rose at least 10 percent.

Last week Square scooped up Caviar, a San Francisco-based restaurant-delivery service, reportedly for $90 million in stock.